Test plating equipment and method



Nov. 19, 1968 J. B. WINTERS 3,412,004

TEST PLATING EQUIPMENT AND METHOD Filed Sept. 10. 1965 2 Sheets-Sheet 1 INVENTOR.

JOHA/ 5. n/m/zzlas' Nov. 19, 1968 J. B. WINTERS 3,412,004

TEST PLATING EQUIPMENT AND METHOD Fild Sept. 10. 1965 2 Sheets-Sheet 2 Q (I) I Q A 0 O O G L) Q United States Patent 0 3,412,004 TEST PLATING EQUIPMENT AND METHOD John B. Winters, Bay Village, Ohio, assignor, by mesne assignments, to Enthone, Incorporated, West Haven, Conn., a corporation of Connecticut Filed Sept. 10, 1965, Ser. No. 486,413 7 Claims. (Cl. 204-195) ABSTRACT OF THE DISCLOSURE Laboratory test electroplating apparatus comprising a container for an electrolyte defined by a bottom wall and upright end and side walls connected thereto and adapted to contain an anode and cathode immersed in the electrolyte, an elongated horizontal recess in the bottom wall, a compressed air-supply tube extending lengthwise within the horizontal recess and of lesser diameter than and spaced apart from the horizontal recess wall, the air supply tube having a plurality of spaced apart, small diameter, air exit holes extending through its surface, and an elongated annular space between the tube and the horizontal recess wall and defined thereby. A vertical elongated slot opening extends upwardly from the top of the horizontal recess or annular space through the top surface of the container bottom wall adjacent a lower edge of the cathode therein. Compressed air emerging from the supply tube exit holes forms relatively small air bubbles in the electrolyte in the annular space, which combine with one another in the annular space to form larger air bubbles. The larger air bubbles grOW to a still larger size in the electrolyte in the vertical elongated slot opening by combining with other air bubbles therein, and such still larger bubbles pass upwardly in random paths through the electrolyte in the container adjacent the cathode surface thereby causing considerable agitation and circulation of the electrolyte adjacent the cathode.

This invention relates to the art of test electroplating and is particularly concerned with a new apparatus and a new method for closely approximating, in a test call, the compressed air induced fiow of electrolyte along a cathode surface which takes place in commercial electroplating tanks.

The apparatus of the present invention comprises, in its broader aspects, a new test cell having a thick tank base in which is formed an elongated recess with a slot leading therefrom through the upper surface of the bottom Wall of the tank adjacent to the lower edge of the cathode and a tube in said recess having a multitude of small outlets for compressed air. The method of this invention broadly comprises the steps of discharging compressed air in a plurality of small streams into an electrolyte in a recess in the base of a plating cell, causing the initially formed small air bubbles to combine with one another and form larger bubbles, and causing circulation of the electrolyte adjacent to the cathode by conducting the larger bubbles 'up through the electrolyte in random paths.

In commercial electroplating tanks, the lower edges of the cathodes are disposed a substantial distance above the bottom wall of the tank and air under pressure is discharged from pipes adjacent to that wall and some distance below the cathode for the purpose of agitating the electrolyte and constantly removing the spent electrolyte in contact with the cathode and replacing it wih fresh electrolyte.

It is to be understood that when metal is being deposited from an electrolyte onto a cathode in such a tank, the electric current depletes the metal being deposited from the parts of the electrolyte in contact with the cathode. Unless this spent electrolyte is replaced the rate and uniformity of deposits varies. The air from the pipes disposed, as stated above, travels upwardly in random paths in bubbles which grow and effectively move the depleted electrolyte away from the cathodes and brings fresh electrolyte into contact therewith.

Laboratory test eqpipment, as constructed heretobefore, has not been capable of reproducing these commercial plating conditions. Since the lower edge of the cathode in such test equipment is on or close to the bottom wall of the cell, the air cannot be discharged from a pipe disposed between the bottom wall and the cathodes, and air under pressure which is discharged above that wall forms small bubbles which travel upwardly in substantial straight lines and without much increase in size. While those bubbles tend to cause some circulation of the electrolyte, they effectively insulate the adjacent portions of the cathode surfaces and often cause the formation of vertical striations or ridges in the deposited plate. Moreover, the insulating effect of these rows of bubbles alters the normally expected current distribution and since the current is thereby varied the extent of depositions is varied. Even when the air streams pass up through small vertical holes in the bottom wall of the cell, there is but little variation of that action of the bubbles.

The present invention provides a new electroplating cell which does not possess the faults of the prior cells and which closely simulates the growth of the air bubbles, the travel in random paths and the satisfactory circulation of the electrolyte with substantial uniformity of deposit. This invention, in method and apparatus, will be better understood by reference to the drawings which accompany this specification and in which:

FIGURE 1 is a top plan view of laboratory test plating equipment embodying the present invention;

FIGURE 2 is a side elevational view of the cell of FIGURE 1;

FIGURE 3 is a perspective view of the cell portion of the apparatus of FIGURES 1 and 2;

FIGURE 4 is a fragmentary cross-sectional view taken on line 44 of FIGURE 1;

FIGURE 5 is a fragmentary cross-sectional view taken on line 55 of FIGURE 1;

FIGURE 6 is a fragmentary view of apparatus embodying the present invention and showing the growth in size and the random paths of travel of the air bubbles in the method embodying the present invention; and

FIGURE 7 is a view similar to FIGURE 6 but showing the behavior of the air bubbles in a conventional test plating tank.

Referring to FIGS. 1 and 2, a cell is designated at 1 and a partial housing 2 is provided therefor. Cell 1 is also shown in FIG. 3 but the housing parts have been removed. The housing includes side plates 5 which extend along opposite sides of the cell flush with the top surface of the cell 1 and extend below the bottom of said base to space the cell base above a supporting surface. The housing also includes an instrument carrying plate 9 connected to the top edges of side plates 5 with one end edge substantially in contact with the adjacent part of the cell. A back plate (not shown) is slidably positioned in opposed faces of the side p]ates..A bottom plate (not shown) is-secured against the bottom of the cell and cooperates with the side and back plates of the housing to enclose the electrical connections presently to be described.

The cell 1 and housing 2 may be composed of any suitable material but, for various reasons, plastic material is preferred. Lucite is quite satisfactory for cell 1 since it is transparent and permits visual observation of what is taking place in the electrolyte. The housing 2 is preferably composed of opaque Lucite. When the cell and housing are composed of Lucite the parts may be readily cemented together by using a cement consisting essentially of ethylene chloride and anhydrous acetic acid. Any other suitable plastic may be used in constructing the cell and housing, for example, chlorinated polyvinyl chloride may be used although it is not transparent. The parts may be cemented together by heat fusion by employing heated air for the purpose.

Cell 1 comprises a thick base and vertical ends 17 and 19 and sides 21 and 23. These ends and sides are fixed to the body 1 in any suitable manner and define a space of the electrolyte.

The cell base 15 is provided with a horizontal recess 25 extending thereinto from one end thereof and opening vertically upward through the upper surface of the base into the space for electrolyte 26. A heating element 27 is disposed in recess 25 and is connected to a source of current through means presently to be described. Any suitable means (not shown) may be employed to prevent leakage of liquid out of the cell through the recess 25 and around the heater.

As is shown in FIGS. 4 and 5, the base 15 is also provided with an elongated cylindrical recess 31 and a vertical passage 32 extending therefrom into the electrolyte space below the inner surface of end wall 19. A tube 33 is attached to the base 15 and extends outwardly therefrom and constitutes an extension of the recess 31. An elongated cylindrical tube 35 closed at its inner end is positioned centrally in recess 31 and spaced apart from the walls of recess 31. This tube 35 projects outwardly through tube 33. Means to prevent leakage of electrolyte from recess 31 and around tube 35 is shown at 41 and is in the form of a rubber tube which is stretched around the end of tube 33 and extends along the outer end of tube 35 in close contact therewith. A compressed air tube 39 is preferably expanded over the outer end of tube 41.

Tube 35 is provided with a plurality of minute radial holes 45 extending through its side wall and spaced apart longitudinally thereof. These holes as shown in FIGS. 4 and 5 are in substantial alignment longitudinally but it will be understood that they need not be longitudinally aligned. Furthermore, these holes are shown as opening downwardly into the space 31 and while that is a preferred position, satisfactory results may be obtained when at least some of these holes 45 extend horizontally or at other angles to the vertical. The vertical passage 32 is narrow and long and rises from the top of recess 31. Hence, bubbles of air discharged from tube 35 may contact and merge with other bubbles and may flow in random paths, as contrasted with prior test equipment when the air flows in small, spaced holes in the base.

While the recess 31, passage 32, tube 35 and holes 45 may vary somewhat in dimensions, the following set of dimensions which have given good results are typical. The recess 31 may be in diameter with its upper side about 1'' below the top surface of base 15. The passage 32 may be about A wide for substantially its full length and the edge thereof adjacent to the inner surface of end wall 19 should be approximately in vertical alignment with the exposed surfaces of a cathode which is positioned along and in substantial contact with end wall 19. The tube 35 may be about A" in outside diameter and about A" in inside diameter and the holes 45 through the tube side wall may be drilled on about /2" centers and the first three or four holes beginning at the inlet end of the tube may be about 0.014" in diameter and the several, for example six, remaining holes will be about .021" in diameter. The volume of air used is preferably about 5 cubic feet per minute but may range from about 2 to about 8 cubic feet.

While holes 45 are shown as extending vertically down through the side wall of tube 35, it is to be understood that the holes may extend at any other desired angle, although better results are obtained when the holes extend downwardly, i.e., below the horizontal; and that the holes may extend outwardly at various angles, as desired.

When the cell just described is to be used for test plating, an anode is placed in close to, but out of contact with, the inner surface of end wall 17 and the cathode is placed in substantial contact with the opposed inner surface of end wall 19. The anode may be maintained in place by a support in the form of a U-shaped conductive wire (not shown) which hooks over the end wall and under the lower edge of the anode. The cathode may be maintained in place by engagement with the side walls 21 and 23. When the electrode and electrolyte have been placed in the cell and the compressed air is admitted into tube 35, it passes out through holes 45 and into recess 31 and forms small bubbles in electrolyte 26. These bubbles combine and grow as they rise around tube 35 and maintain considerable size before they emerge from passage 35 and come into close contact with the cathode. Since the large bubbles are formed by the combining of a plurality of small ones, the growing bubbles follow random paths and cause considerable agitation of the electrolyte. This action is indicated in FIG. 6 where the different sizes and the random paths of travel of the bubbles are shown. These bubbles of air exert little, if any, insulating effect on the cathode and any such effect which does occur is in a constant state of change of position due to the random paths of travel of the bubbles so that, as a result, the uniformity of deposition of metal on the cathode is not appreciably effected. The rather violent agitation of the electrolyte insures that fresh liquid containing a supply of metal to be deposited will be constantly in contact with the cathode. In this manner, substantially uniform deposition of metal over the entire cathode surface is obtained and there is substantially no formation of striations or streaks in the plate such as was characteristic of the prior test equipment.

In FIG. 7 is shown a conventional test cell. In this figure the base of the cell has an elongated recess from which a plurality of small holes 53 extend upwardly and open into the space occupied by the electrolyte 53 at one side of the cathode. Compressed air is released into one end of the recess and escapes through holes 53 into the electrolyte where it forms small bubbles which flow upwardly in separate paths. These bubbles grow only slightly in size, travel in straight lines close to the cathode and tend to shield the adjacent surfaces of the cathode with the result that there is less metal deposited behind these streams of air than at other places. The result in the finished plate is a plurality of low spots, streaks or striations in which less metal has been deposited than elsewhere. This condition and these results are avoided by the present invention.

Reference was made above to the instrument carrying plate 9, a bottom plate and electrical connections. Since such parts are ancillary to the present invention and are not being claimed they will be described only briefly.

The electrical heater 27 is connected in a power circuit with a pilot light 60 to indicate whether the bath is at the desired temperature and a thermostatic temperature control including a Vernier 61. Conductors 65 supply current to parts 27, 60 and 61.

Having thus described this invention in such full, clear concise and exact terms as to enable any person skilled in the art to which it pertains to make and use the same, and having set forth the best mode contemplated of carrying out this invention, I state that the subject matter which I regard as being my invention is particularly pointed out and distinctly claimed, it being understood that equivalents or modifications of, or substitutions for, parts of the above specifically described embodiment of the invention may be made without departing from the scope of the invention as set forth in what is claimed.

What is claimed is:

1. In a laboratory test electroplating apparatus comprising a container for an electrolyte defined by a bottom wall and upright end and side walls connected thereto and adapted to contain an anode and a cathode spaced apart from the anode immersed in the electrolyte, an elongated horizontal recess in said bottom wall, means for supplying compressed air to said horizontal recess, and means for conducting compressed air in the form of air bubbles from the horizontal recess to the interior of the container adjacent the surface of the cathode, the improvement whereby insulation of the cathode surface by rows of small air bubbles with attendant formation of striations in the metal electroplate on the cathode is substantially eliminated and a substantially uniform, striation-free metal electroplate is obtained on the cathode, which comprises as the compressed air conducting means and supplying means a vertical elongated slot opening extending upwardly from the top of said recess through the top surface of said container bottom wall adjacent a lower edge of the cathode therein and adapted to contain electrolyte, a compressed air-supply tu-be extending lengthwise within the horizontal recess and of lesser diameter than and spaced apart from the horizontal recess wall thus forming an elongated annular space adapted to contain electrolyte between the tube and the horizontal recess wall and defined thereby, said tube having a plurality of spaced apart, small diameter, air exit holes extending through its side Wall whereby relatively small air bubbles formed in the electrolyte in the annular space by the compressed air emerging from the tube exit holes combine with one another in the annular space electrolyte to form larger air bubbles and the larger air bubbles grow to a still larger size in the electrolyte in the vertical elongated slot opening by combining therein with other air bubbles, such still larger air bubbles passing upwardly through the electrolyte adjacent the cathode surface in random paths causing considerable agitation of and circulation of the electrolyte adjacent the cathode surface.

2. The combination of elements set forth in claim 1 in which the said tube is positioned substantially coaxially in said recess.

3. The combination of elements set forth in claim 1 in which the said holes extend downwardly through the side wall of the tube.

4. The combination of elements set forth in claim 1 in which the said bottom wall has a cylindrical tube aligned with said recess to receive the said air tube and means surrounds the ends of said tubes to prevent escape of electrolyte from the recess.

5. The combination of elements set forth in claim 1 in which several of the holes near the inlet end of the tube are smaller in diameter than those more remote from the inlet end.

6. The combination of elements set forth in claim 5 in which said holes extend downwardly through the tube side wall.

7. The combination of elements set forth in claim 6 in which the said bottom wall has a cylindrical tube through which the tube for compressed air extends and in which means surrounds the ends of said tubes to prevent escape of electrolyte from the recess.

References Cited UNITED STATES PATENTS 1,249,787 12/1917 Leuchter 204 -277 1,260,830 3/1918 Studt 204-277 XR 1,423,815 7/1922 Park 204-277 XR 1,788,462 1/ 1931 Johnstone 204277 2,145,745; 1/ 1939 Armstrong et al. 204-277 XR 2,760,928 8/1956 Ceresa 204 3,259,049 7/ 1966 Uithover 204-277 XR HOWARD S. WILLIAMS, Primary Examiner.

D. R. JORDAN, Assistant Examiner. 

